Method for converting perylen-3,4:9,10-tetracarboxylic acid diimides into a form suitable for use as a fluorescent dye

ABSTRACT

A process for converting perylene-3,4:9,10-tetracarboximides of the general formula I 
     
       
         
         
             
             
         
       
     
     in which R 1  and R 2  are each unbranched, branched or cyclic C 1 -C 8 -alkyl to a form suitable for use as fluorescent dyes, which comprises
     a) dissolving or suspending the perylene-3,4:9,10-tetracarboximides whose molecules have a molecular volume of ≦230 Å 3  in an organic or inorganic solvent at from 0 to 250° C.,   b1) cooling the solution obtained in step a) to or below the crystallization temperature and, in the case of an organic solvent, if desired at the same time removing excess solvent until the first crystals form, or, in the case of an inorganic solvent, adding water or dilute aqueous solutions of the solvent until the first crystals form, and maintaining the solution at this temperature for further crystallization or   b2) cooling the suspension obtained in step a) to or below the crystallization temperature when the temperature in step a) was above the crystallization temperature, and maintaining the suspension at this temperature for further crystallization,   c) isolating the solvate crystals formed in step b) and   d) then removing the solvent from the solvate crystals,
 
and also novel crystalline forms of perylene- 3,4:9,10 -tetracarboxylic diimides.

BACKGROUND OF THE INVENTION

The present invention relates to a novel process for convertingperylene-3,4:9,10-tetracarboximides of the general formula I (referredto hereinbelow as “perylimides I” for short)

in which R¹ and R² are each unbranched, branched or cyclic C₁-C₈-alkyl,to a form suitable for use as fluorescent dyes.

The invention also relates to crystalline solvates of the perylimides Iwhich contain 1 or 2 mol of solvent per mole of perylimide I.

The invention further relates to different crystalline forms ofN,N′-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboximide whichare characterized by X-ray powder diagrams (CuK_(α)) having significantlines at the following d values:

Form A (“perylimide A”): 10.2, 9.60, 8.17, 7.60, 7.07, 6.89, 6.02, 5.64,4.89, 4.79, 4.63, 3.93, 3.81, 3.53 and 3.43 Å;Form B (“perylimide B”): 15.3, 7.68, 7.32, 7.15, 5.99, 5.59, 5.33, 4.98,4.24, 3.86 and 3.235 Å;Form C (“perylimide C”): 10.67, 9.88, 9.36, 7.82, 7.16, 6.89, 5.74,5.49, 4.68, 4.085, 3.354 and 3.252 Å;Form D (“perylimide D”): 9.7, 8.6, 7.85, 6.88, 4.83, 4.13 and 3.81 Å;Form E (“perylimide E”): 15.2, 14.7, 8.04, 7.76, 7.36, 6.43, 5.59, 4.99,4.25, 4.14 and 3.863 Å.

The invention relates not least to the use of the perylimides I and theperylimides A to E prepared according to the invention as fluorescentdyes for coloring organic and inorganic polymeric materials, and also asemitter materials in electrooptical components.

EP-A-55 363 describes various perylimides which are substituted on bothimide nitrogen atoms by alkyl- or chlorine-substituted phenyl, includingN,N′-bis(2,6-diisopropylphenyl)perylimide.

These perylimides are prepared by reactingperylene-3,4:9,10-tetracarboxylic dianhydride with the correspondinglysubstituted aniline in the presence of a zinc compound and sometimesalso of acetic acid as a catalyst in quinoline. The perylimides are thenprecipitated by adding methanol, filtered off and washed with methanoland water. To remove unconverted perylene-3,4:9,10-tetracarboxylicdianhydride, the perylimides isolated in this way are usually thenstirred in hot carbonate solution.

EP-A-55 363 proposes a further variant for isolating the perylimides inwhich the entire reaction mixture is initially brought into solution byadding a solvent which dissolves the perylimide, such asN-methylpyrrolidone, dimethylacetamide or dimethylformamide, andheating, the solution is filtered and the perylimide is precipitated outagain by adding lower alcohols, such as methanol, optionally in amixture with water. The perylimides should usually be obtained in asufficiently pure form.

However, according to in-house investigations, this method ofprecipitation results only in products of insufficient purity beingobtained which contain by-products, in particular N-substitutedperylene-3,4-dicarboximide, in relatively large amounts(generally >10%), and are substantially X-ray-amorphous, and also finelycrystalline and difficult to filter.

For further purification, EP-A-55 363 proposes reprecipitation fromsulfuric acid and also recrystallization, without giving any furtherinformation.

It is an object of the present invention to provide a process whichmakes it possible to efficiently purify perylimides I and in which theperylimides I are obtained directly in a form suitable for use asfluorescent dyes.

We have found that this object is achieved by a process for convertingperylene-3,4:9,10-tetracarboximides of the general formula I

in which R¹ and R² are each unbranched, branched or cyclic C₁-C₈-alkylto a form suitable for use as fluorescent dyes, which comprises

-   a) dissolving or suspending the perylene-3,4:9,10-tetracarboximides    whose molecules have a molecular volume of ≦230 Å³ in an organic or    inorganic solvent at from 0 to 250° C.,-   b1) cooling the solution obtained in step a) to or below the    crystallization temperature and, in the case of an organic solvent,    if desired at the same time removing excess solvent until the first    crystals form, or, in the case of an inorganic solvent, adding water    or dilute aqueous solutions of the solvent until the first crystals    form, and maintaining the solution at this temperature for further    crystallization or-   b2) cooling the suspension obtained in step a) to or below the    crystallization temperature when the temperature in step a) was    above the crystallization temperature, and maintaining the    suspension at this temperature for further crystallization,-   c) isolating the solvate crystals formed in step b) and-   d) then removing the solvent from the solvate crystals.

It is essential to the process according to the invention that thesolvent molecules used in step a) have a molecular volume of ≦230 Å³,preferably ≦200 Å³ and more preferably ≦180 Å³, and are therefore ableto form stable binary crystal phases (solvates or else clathrates) withthe perylimide I which contain up to 2 molecules of solvent per moleculeof perylimide I.

The molecular volumes specified may be calculated from the structure ofthe molecule by the method published by Gavezzotti (J. Amer. Chem. Soc.1989, 11, p. 1835).

Preference is given to using solvents in which the perylimide Idissolves, optionally after heating, although solvents may also be usedin which the perylimide I only partially dissolves at the treatmenttemperature. The conversion to the corresponding solvates is theneffected in suspension.

Accordingly, useful organic solvents are in particular (the term alkylis also intended to encompass cycloalkyl, in particular cyclohexyl):

-   -   di-C₁-C₄-alkylsulfoxides, such as dimethyl sulfoxide;    -   sulfolane;    -   unsubstituted and N—C₁-C₆-alkyl-substituted C₄-C₆-lactams, such        as pyrrolidone, N-methylpyrrolidone, N-cyclohexylpyrrolidone,        N-octylpyrrolidone, caprolactam and N-ethylcaprolactam;    -   unsubstituted and N—C₁-C₆-alkyl-substituted aliphatic        C₁-C₆-carboxamides, such as formamide, dimethylformamide,        dimethylacetamide, benzamide and N-acetylmorpholine;    -   aliphatic nitriles having from 2 to 12 carbon atoms, such as        acetonitrile and 2-methoxypropionitrile;    -   aromatic nitriles which may be substituted by C₁-C₈-alkyl,        C₁-C₈-alkoxy and/or halogen, such as benzonitrile and        3-methylbenzonitrile;    -   aliphatic C₁-C₁₂-carboxylic acids and their C₁-C₆-alkyl esters        having a total number of carbon atoms of ≦12, such as formic        acid, acetic acid, propionic acid, 2-ethylhexanoic acid and        ethyl acetate;    -   hydroxy-C₂-C₆-carboxylic acids and their esters, such as lactic        acid, butyrolactone, valerolactone and caprolactone;    -   C₂-C₆-alkylene carbonates, such as ethylene carbonate and        propylene carbonate;    -   benzoic acids, such as benzoic acid, phthalic acid and        terephthalic acid;    -   naphthoic acids, such as α- and β-naphthoic acid;    -   C₁-C₆-alkyl benzoates, such as methyl benzoate and ethyl        3-methylbenzoate;    -   di-C₁-C₂-alkyl phthalates, such as diethyl phthalate;    -   monohydric and polyhydric, saturated and unsaturated, aliphatic        and cycloaliphatic C₄-C₁₂-alcohols, such as butanol, isoamyl        alcohol, cyclohexanol, octanol, 3-methyl-1-pentyn-3-ol,        methoxypropanol, furfuryl alcohol, tetrahydrofurfuryl alcohol        and 1,5-pentanediol;    -   araliphatic alcohols, such as benzyl alcohol, 2-phenylethanol        and 4-methoxybenzyl alcohol;    -   mono- and oligo-C₂-C₃-alkylene glycol mono- and -di-C₁-C₈-alkyl-        and monophenyl ethers, such as ethylene glycol monomethyl ether,        ethylene glycol monobutyl ether, ethylene glycol monophenyl        ether and diethylene glycol dimethyl ether;    -   aliphatic C₃-C₁₂-ketones, such as acetone, methyl isobutyl        ketone, diacetone alcohol, cyclohexanone and        2-methylcyclohexanone;    -   aromatic ketones which may be substituted by C₁-C₈-alkyl,        C₁-C₈-alkoxy and/or halogen, such as isophorone, acetophenone,        propiophenone, 3-chloroacetophenone and 3-ethylacetophenone;    -   aliphatic and cycloaliphatic C₄-C₁₂-ethers, such as methyl        tert-butyl ether, ethyl isobutyl ether, 2-ethylhexyl methyl        ether, tetrahydrofuran and dioxane;    -   aromatic ethers which may be substituted by C₁-C₈-alkyl,        C₁-C₈-alkoxy and/or halogen, such as diphenyl ether;    -   heterocycles, such as pyridine, picoline, lutidine, quinoline,        methylquinoline, imidazole, methylimidazole and        1,3-dimethyl-2-imidazolidinone;    -   aromatic hydrocarbons which may be substituted by C₁-C₈-alkyl,        C₁-C₈-alkoxy, C₁-C₆-alkylamino, di-C₁-C₃-alkylamino, chlorine        and/or nitro, such as toluene, o-, m- and p-xylene,        ethylbenzene, cumene, methoxybenzene, chlorobenzene,        o-dichlorobenzene, 1,2,4-trichlorobenzene, nitrobenzene, phenol,        3-methylphenol, p-chlorophenol, o-nitrophenol,        N-hydroxyethylaniline, 1,2,3,4-tetrahydronaphthalene,        2-chloronaphthalene, 2-methoxynaphthalene and        dimethylnaphthalene;    -   aliphatic and cycloaliphatic C₆-C₁₈-hydrocarbons, such as        limonene, decalin and methylcyclohexane;    -   chlorohydrocarbons, such as methylene chloride, chloroform,        tetrachloromethane, dichloroethane, trichloroethane and        tetrachloroethane.

It will be appreciated that mixtures of these solvents may also be used.

Preferred organic solvents are xylene, toluene, N-methylpyrrolidone,dimethylacetamide, dimethylformamide, methyl isobutyl ketone, methylenechloride, ethylene glycol monophenyl ether and ethylene glycol monobutylether.

It is also possible to use combinations of these solvents, i.e. toinitially form a solvate with a first solvent (for exampleN-methylpyrrolidone) and to exchange the solvent in this solvate bytreating with a second solvent (for example acetic acid).

Useful inorganic solvents are in particular acids, in particularsulfuric acid.

In step a) of the process according to the invention, the perylimide Iis either dissolved in the solvent or suspended therein.

Accordingly, when organic solvents are used, the procedure in accordancewith the invention may be as follows: a mixture of perylimide I andsolvent is heated to a temperature at which the perylimide I dissolvesin the solvent, the resulting solution is then cooled in step b1) to orbelow the crystallization temperature of the perylimide I and thesolution is maintained at this temperature for further crystallization;the crystallization may, if desired, be promoted by at the same timeremoving excess solvent. Or the perylimide I is suspended in thesolvent, preferably at elevated temperature, to increase the purifyingeffect, the resulting suspension is then cooled in step b2) to or belowthe temperature at which the solvate crystals crystallize out and thesuspension is maintained at this temperature for furthercrystallization.

When inorganic solvents are used, the procedure may similarly be asfollows: the perylimide I is dissolved at a suitable temperature insubstantially anhydrous to highly concentrated solvent and thecrystallization is initiated in step b1) by diluting the solvent withwater or aqueous solutions of the solvent. Or the perylimide I isstirred directly for several hours in a less concentrated solvent,preferably at temperatures around room temperature, likewise resultingin the formation of solvate crystals.

This will now be illustrated in detail using the example of theparticularly preferred solvent sulfuric acid. In the first variant, itis advisable to dissolve the perylimide I at approximately roomtemperature (approx. 20-30° C.) in about 96 to 100% by weight sulfuricacid, then to gradually reduce the sulfuric acid concentration by addingwater or more dilute sulfuric acid (for example 20% by weight sulfuricacid) to about 70 to 93% by weight and thus effect the crystallizationof a sulfate of the perylimide I. In the second variant, about 70 to 90%by weight sulfuric acid is used directly.

Depending on the molecular size of the solvent, the crystalline solvateswhich are obtained in step c) of the process according to the inventionand are likewise according to the invention have a molar composition ofsolvent to perylimide I of 1:1 (for example in the case of xylene,N-methylpyrrolidone, methoxybenzene and dimethylacetamide solvates) or2:1 (for example in the case of methylene chloride and acetic acidsolvates). Despite the same gross composition, the crystalline phasesmay have different crystal structures. In the case of some of thesesolvates (for example in the case of methylene chloride and acetic acidsolvates), the solvent molecules may leave the perylimide host latticewithout its crystalline structure changing significantly. In such cases,nonstoichiometric binary phases of solvent and perylimide I may also beformed.

The exact composition of the sulfuric acid solvates generally cannot bedetermined, since the solvates rapidly lose sulfuric acid when isolated.However, characterization by X-ray powder diffractometry is just aspossible as in the case of the solvates with organic solvents.

The solvent is then removed from the solvate crystals in step d),resulting substantially in the retention of the crystalline structuresformed in step b) or else the formation of new crystalline phases. Thesolvent is advantageously removed by drying solvate crystals, optionallyunder reduced pressure and at elevated temperature. If desired, thesolvate crystals may have been additionally treated (washed) beforedrying, with a solvent which itself does not form a solvate, preferablywith water or mixtures of organic solvents with water.

The crystalline forms of the perylimides I obtained according to theinvention may be characterized by X-ray powder diffractometry or bysingle crystal structural analysis. This resulted in the crystallineperylimides A to E which are likewise according to the invention beingfound, which are obtainable by crystallization from methylene chloride(perylimide A), acetic acid (perylimide B), sulfuric acid (perylimides Cand D) and M-methylpyrrolidone/acetic acid (perylimide E). The X-raypowder diagrams of these perylimides are depicted in FIGS. 1 and 3 to 6.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the x-ray powder diagram of crystalline perylimide A.

FIG. 2 illustrates the x-ray powder diagram of NMP-dampened crystallineperylimide Ia.

FIG. 3 illustrates the x-ray powder diagram of crystalline perylimide B.

FIG. 4 illustrates the x-ray powder diagram of crystalline perylimide C.

FIG. 5 illustrates the x-ray powder diagram of crystalline perylimide D.

FIG. 6 illustrates the x-ray powder diagram of crystalline perylimide E.

The process according to the invention has a series of advantages whichcould not have been predicted. For instance, not only was it made easierto crystallize the perylimides I, but coarsely crystalline crystals werealso formed which are easy to filter, can be washed without significantproduct loss and additionally have high purities of generally >90%(by-products formed in the synthesis such as N-monoalkylation productscan be removed without any problem). The use of sulfuric acid as solventgenerally allows the degree of purity to be further increased to >95% byadditional removal of decarboxylation products occurring in thesynthesis, so that, irrespective of the way in which the crude materialsI used are synthesized, product qualities can be obtained in a simplemanner which are otherwise only obtainable by chromatography. Thecrystals formed are notable not least for their high dissolution rateswhich allow them to be particularly readily incorporated into plastics.

Accordingly, the perylimides I obtained according to the invention, inparticular the perylimides A to E, have outstanding suitability asfluorescent dyes for coloring organic and inorganic polymeric materialsand also as emitter materials in electrooptical components, for exampledisplays and emissive color filters, for which the perylimide A inparticular is suitable owing to its marked solid state fluorescence.

EXAMPLES Conversion ofN,N′-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboximide(perylimide Ia) in a Form Suitable for Use as a Fluorescent Dye Example1

6 g of the perylimide Ia were dissolved in 800 ml of boiling methylenechloride and stirred for a further 60 min at the boiling temperature ofthe solvent. After filtration under pressure via a G4 glass frit, thefiltrate was stirred under reflux for a further 60 min and then cooledby heat exchange with the environment to room temperature (approx. 20°C.). A vacuum of approx. 50 kPa was then applied at this temperature togradually remove methylene chloride until the first crystals formed. Themixture was then cooled to −20° C. After storing for one day at thistemperature, the crystals formed were filtered off, washed with coldmethylene chloride and dried at 20° C.

X-ray structural analysis at 203 K showed a solvate having 2 moleculesof methylene chloride per molecule of perylimide Ia having the followingcrystallographic data: space group P 2₁/n, Z=2, a=1003.2(2) pm,b=1907.8(6) pm, c=1156.3(2) pm, β=96.794(10)°, R1=0.1151, wR2=0.2308.

Complete removal of the methylene chloride under reduced pressure gavethe perylimide Ia in the crystalline form A (perylimide A) havingsignificant lines in the X-ray powder diagram (CuK_(α)) at the followingd values (FIG. 1): 10.2, 9.60, 8.17, 7.60, 7.07, 6.89, 6.02, 5.64, 4.89,4.79, 4.63, 3.93, 3.81, 3.53 and 3.43 Å. Rietveld refinement of thepowder diagram resulted in the following crystallographic data beingobtained for the perylimide A: space group P 2₁/c, Z=2, a=1207.3(3) pm,b=1918.3(5) pm, c=1433.1(4) pm, β=141.10(1)°, R1=0.1615, wR2=0.2041.

Example 2

10.1 g of a mixture of 6 parts of the perylimide Ia and 4 parts ofN-(2,6-diisopropylphenyl)perylene-3,4-dicarboximide were dissolved in 1200 ml of p-xylene in the heat of boiling. After filtration at thistemperature via a G4 glass frit, the filtrate was cooled to roomtemperature and concentrated to half its volume at 20° C. by passing agentle air stream over it. After formation of the first crystals, thevessel was sealed. The red rhombohedra formed after 8 d were filteredoff and washed with a little cold petroleum ether.

No N-(2,6-diisopropylphenyl)perylene-3,4-dicarboximide could be detectedin the crystals by chromatography, which shows that the processaccording to the invention makes it possible to effectively remove thedecarboxylation products from crude materials of the perylimides I.

X-ray structural analysis showed a solvate of perylimide Ia withp-xylene in a molar ratio of 1:1 having the following crystallographicdata: space group P ca2₁, a=1825.1(3) pm, b=830.9(1) pm, c=2988.9(5) pm,R1=0.0638, wR2=0.1682.

Example 3

A mixture of 3 g of the perylimide Ia and 30 ml of N-methylpyrrolidone(NMP) was stirred at 80° C. for 8 d. After cooling to 20° C., theresulting crystal slurry was filtered off and washed briefly with coldNMP.

The X-ray powder diagram (CuK_(α)) of the NMP-damp crystalline producthad significant lines at d values of 15.3, 8.36, 7.64, 7.36, 6.48, 5.95,5.85, 5.65, 5.56, 5.10, 4.36, 4.14 and 3.87 Å (illustrated in FIG. 2).The comparison of the X-ray powder diagrams of Example 2 and Example 3gave the isomorphicity of the two solvates.

The crystals dried under gentle conditions lost a total of 12.1% oftheir weight under thermal treatment at 201-218° C., which correspondsto the loss of 1 mol of NMP from a solvate of molar composition 1:1(calc. 12.2% by weight).

Elemental analysis (% by weight calc./found): C, 78.6/78.2; H, 6.4/6.8;N, 5.2/5.2; O: 9.9/10.4.

Comparative Example C

6 g of the perylimide Ia were dissolved in 200 ml of NMP at 100° C.After stirring for 20 minutes at this temperature, the solution wasfiltered at 100° C. and poured into 2 000 ml of a 1:1 mixture (v/v) ofmethanol and water within 5 min with vigorous stirring.

The red, voluminous precipitate which precipitated out was filtered off,washed with water and dried under reduced pressure at 100° C. for 24 h.

The X-ray powder diagram of the material obtained only showed 4 broadlines whose average d values (15.7, 6.95, 5.88, 3.47 Å) correspond tothe molecular dimensions of the perylimide Ia and it therefore proved tobe substantially X-ray-amorphous.

Example 4

A mixture of 2 g of the perylimide Ia and 50 ml of glacial acetic acidwas stirred at room temperature for 14 h. The crystals were filtered offand separated into two halves.

One half was dried under air at room temperature. The X-ray powderdiagram (CuK_(α)) of the product dried in this way had significant linesat d values of 14.7, 8.64, 7.73, 7.27, 6.69, 6.14, 5.75, 5.68, 4.98,4.54, 4.49, 4.35, 4.13 and 3.87 Å.

Thermal treatment at 115-196° C. resulted in the crystals dried underair losing a total of 13.8% of their weight, which corresponds to theloss of 2 mol of acetic acid from a solvate of the molar composition 2:1(calc. 14.4%).

The other half was dried under reduced pressure at 80° C. This resultedin acetic acid-free perylimide Ia being obtained in the crystalline formB (perylimide B) having significant lines in the X-ray powder diagram(CuK_(α)) at the following d values (FIG. 3): 15.3, 7.68, 7.32, 7.15,5.99, 5.59, 5.33, 4.98, 4.24, 3.86 and 3.235 Å.

Example 5

3 g of the perylimide Ia were dissolved in 50 ml of methoxybenzene inthe heat of boiling. The solution was then initially cooled gradually toroom temperature and then cooled further in an ice bath. The crystalswere filtered off, washed with a little cold methoxybenzene and dried atroom temperature and a pressure of 10 kPa for 24 h.

The X-ray powder diagram of the perylimide Ia present in the form ofshiny platelets suggested that there was a mixture of different solvatephases of the molar composition 1:1. Grinding with a mortar resulted ina further change in the line positions, while the composition remainedunchanged.

Elemental analysis (% by weight calc./found): C, 80.7/80.4; H, 6.2/6.1;N, 3.4/3.4; O: 9.8/9.7.

Example 6

2 g of the perylimide Ia were dissolved in 150 ml of dimethylacetamidein the heat of boiling. The solution was then gradually cooled to roomtemperature. After storing for three days at room temperature, thecrystals were filtered off, washed with a little cold dimethylacetamideand dried at room temperature and a pressure of 10 kPa for 24 h.

Elemental analysis of the perylimide Ia present in the form of shinyplatelets showed a solvate of molar composition 1:1 whose X-ray powderdiagram (CuK_(α)) showed significant lines at the following d values:15.2, 7.60, 7.35, 6.46, 5.07, 4.34, 3.87 and 3.47 Å.

Elemental analysis (% by weight calc./found): C, 78.3/77.9; H, 6.4/6.4;N, 5.3/5.4.

Example 7

2 g of the perylimide Ia were dissolved in 40 g of oleum (100% by weightsulfuric acid) at room temperature. After stirring for 15 minutes, thesulfuric acid concentration was reduced to 82% by weight by metering ina total of 10.2 ml of 20% by weight sulfuric acid within 120 min whilemaintaining a temperature of 25-30° C. The resulting crystal suspensionwas stirred at 20° C. for 48 h and then filtered through a G4 glassfrit.

The resulting red crystals which were damp with sulfuric acid werecharacterized with exclusion of air by a Debye-Scherrer diagram. Therewere significant lines at the following d values: 10.24, 7.80, 6.77,6.24, 5.61, 5.34, 4.58, 4.42, 4.01, 3.805 and 3.415 Å.

A similar experimental procedure and the setting of end sulfuric acidconcentrations of 80% by weight, 84% by weight and 86% by weightresulted in crystals having identical X-ray powder diagrams beingobtained.

Example 8

A mixture of 2 g of the perylimide Ia and 40 g of 84% by weight sulfuricacid was stirred at 20° C. for 48 h. The resulting crystal slurry wasfiltered through a G4 glass frit.

The resulting red crystals which were damp with sulfuric acid werecharacterized with exclusion of air by a Debye-Scherrer diagram(CuK_(α)). There were significant lines at the following d values:10.24, 7.80, 6.77, 6.24, 5.61, 5.34, 4.58, 4.42, 4.01, 3.805 and 3.415Å.

A similar experimental procedure and the setting of end sulfuric acidconcentrations of 86% by weight and 90% by weight resulted in crystalshaving identical X-ray powder diagrams being obtained.

Example 9

A mixture of 2 g of the perylimide Ia and 40 g of 82% by weight sulfuricacid was stirred at 20° C. for 48 h. The resulting crystal slurry wasfiltered through a G4 glass frit.

The resulting red crystals which were damp with sulfuric acid werecharacterized with exclusion of air by a Debye-Scherrer diagram(CuK_(α)). There were significant lines at the following d values: 9.74,9.27, 7.73, 7.13, 5.80, 4.7 and 4.11 Å.

A similar experimental procedure and the setting of end sulfuric acidconcentrations of 80% by weight resulted in crystals having identicalX-ray powder diagrams being obtained.

Example 10

12.5 g of the perylimide Ia were dissolved in 250 g of oleum (100% byweight sulfuric acid) at room temperature. After stirring for 15minutes, the sulfuric acid concentration was reduced to 92.4% by weightby metering in a total of 23 ml of 20% by weight sulfuric acid within300 min while maintaining a temperature of 25-30° C. The resultingcrystal suspension was stirred for 4 h and then filtered through a G4glass frit. The crystal slurry was spread out thinly and hydrolyzedunder air for 12 h. During this time, the sulfuric acid took up furtherwater. After stirring the crystal suspension in 500 ml of water, thecrystals were filtered off, washed to neutrality with water and dried toconstant weight at 80° C.

The crystalline form C of the perylimide Ia (perylimide C) was obtainedin the form of dark orange-colored crystals having significant lines inthe X-ray powder diagram (CuK_(α)) at the following d values (FIG. 4):10.67, 9.88, 9.36, 7.82, 7.16, 6.89, 5.74, 5.49, 4.68, 4.085, 3.354 and3.252 Å.

Example 11

9.6 kg of the perylimide Ia were introduced into 144 kg of concentratedsulfuric acid (96% by weight) with vigorous stirring within 20 min. Thestirring was continued for 90 min at an internal temperature of 28° C.until complete dissolution. The sulfuric acid concentration was thenreduced to 92% by weight by metering in 6.2 kg of water within 240 min.The resulting crystal slurry was filtered off, washed three times with10 l of 87% by weight sulfuric acid and then stirred in 70 l of water at50-60° C. for 60 min. The crystal slurry was filtered off, washed toneutrality with water and dried to constant weight at 100° C.

The crystalline form D of the perylimide Ia (perylimide D) was obtainedin the form of dark orange-colored crystals having significant lines inthe X-ray powder diagram (CuK_(α)) at the following d values (FIG. 5):9.7, 8.6, 7.85, 6.88, 4.83, 4.13 and 3.81 Å.

Example 12

23 g of the 1:1 solvate of the perylimide Ia with NMP (Example 4) werestirred under reflux in 146 g of glacial acetic acid for 15 h. Thecrystal suspension was allowed to cool to 70-80° C. The crystal slurrywas then filtered off, and washed initially with 32 g of glacial aceticacid at 60-70° C., then with 140 ml of water and afterwards with 500 mlof 2% by weight ammonia solution. After washing to neutrality with waterand driving out the water with ethanol, the filter cake was dried at100° C.

The crystalline form E of the perylimide Ia (perylimide E) was obtainedin the form of orange-colored crystals having significant lines in theX-ray powder diagram (CuK_(α)) at the following d values (FIG. 6): 15.2,14.7, 8.04, 7.76, 7.36, 6.43, 5.59, 4.99, 4.25, 4.14 and 3.863 Å.

Examples 13 to 21

2 g of the perylimide Ia were dissolved in x ml of the solvent L at T°C. Undissolved starting material was filtered off at T° C. The filtrateswere cooled to room temperature within t h. The orange to orange-redcrystals formed were filtered off and dried under reduced pressure atroom temperature.

Further details of these experiments and also the d values of thesignificant lines in the particular X-ray powder diagrams are compiledin the following table.

TABLE x T t d values Ex. [ml] L [° C.] [h] [Å] 13 100 Nitro- 150 4 20.4,11.8, 8.32, 7.81, 7.20, 6.80, benzene 6.49, 6.14, 5.408, 4.947, 4.083,3.927 14 100 Phenyl 150 4 16.1, 14.2, 10.3, 8.48, 7.61, 6.793, glycol5.180, 4.237 15 100 n-Butanol 90 2 14.7, 8.26, 7.47, 6.44, 5.633, 4.879,4.240, 3.923, 3.842, 3.743 16 150 Methyl 60 2 14.7, 14.45, 7.45, 7.31,6.40, 4.834, glycol 4.212, 3.894 17 100 Cyclo- 80 2 11.8, 8.4, 7.17,6.48, 5.89, 5.44, hexanol 5.284, 4.68, 4.49, 3.55 18 100 Chloro- 120 620.5, 13.6, 11.8, 7.75, 7.20, 6.84, benzene 6.58, 6.19, 4.53, 3.956 1950 Benzyl 130 6 15.6, 9.62, 9.28, 8.296, 7.973, alcohol 6.369, 6.045,5.155, 4.462, 4.157, 3.888, 3.353 20 150 Butyl 130 4 7.94, 7.232, 7.12,5.92, 4.96, 4.79, glycol 4.62, 3.986, 3.63, 3.555 21 75 Methyl 130 415.2, 14.8, 14.4, 8.86, 7.82, 6.84, benzoate 6.75, 5.8, 5.00, 4.42

1. A process for converting perylene-3,4:9,10-tetracarboxylic diimidesof the general formula I

in which R¹ and R² are each unbranched, branched or cyclic C₁-C₈-alkylto a form suitable for use as fluorescent dyes, which comprises a)dissolving or suspending the perylene-3,4:9,10-tetracarboxylic diimideswhose molecules have a molecular volume of ≦230 Å³ in an organic orinorganic solvent at from 0 to 250° C., b1) cooling the solutionobtained in step a) to or below the crystallization temperature and, inthe case of an organic solvent, if desired at the same time removingexcess solvent until the first crystals form, or, in the case of aninorganic solvent, adding water or dilute aqueous solutions of thesolvent until the first crystals form, and maintaining the solution atthis temperature for further crystallization or b2) cooling thesuspension obtained in step a) to or below the crystallizationtemperature when the temperature in step a) was above thecrystallization temperature, and maintaining the suspension at thistemperature for further crystallization, c) isolating the solvatecrystals formed in step b) and d) then removing the solvent from thesolvate crystals.
 2. A process as claimed in claim 1, wherein thesolvent used is a di-C₁-C₄-alkyl sulfoxide; a sulfolane; anunsubstituted or N—C₁-C₆-alkyl-substituted C₄-C₆-lactam; anunsubstituted or N—C₁-C₆-alkyl-substituted aliphatic C₁-C₆-carboxamide;an aliphatic nitrile having from 2 to 12 carbon atoms; an aromaticnitrile which may be substituted by C₁-C₈-alkyl, C₁-C₈-alkoxy and/orhalogen; an aliphatic C₁-C₁₂-carboxylic acid or its C₁-C₆-alkyl estershaving a total number of carbon atoms of ≦12; a hydroxy-C₂-C₆-carboxylicacid or its esters; a C₂-C₆-alkylene carbonate; a benzoic acid; anaphthoic acid; a C₁-C₈-alkyl benzoate, a di-C₂-C₄-alkyl phthalate; amonohydric or polyhydric, saturated or unsaturated, aliphatic orcycloaliphatic C₄-C₁₂-alcohol; an araliphatic alcohol; a mono- oroligo-C₂-C₃-alkylene glycol mono- and -di-C₁-C₈-alkyl- and monophenylether; an aliphatic C₃-C₁₂-ketone; an aromatic ketone which may besubstituted by C₁-C₈-alkyl, C₁-C₈-alkoxy and/or halogen; an aliphatic orcycloaliphatic C₄-C₁₂-ether; an aromatic ether which may be substitutedby C₁-C₈-alkyl, C₁-C₈-alkoxy and/or halogen; a heterocycle; an aromatichydrocarbon which may be substituted by C₁-C₈-alkyl, C₁-C₈-alkoxy,C₁-C₆-alkylamino, di-C₁-C₃-alkylamino, chlorine and/or nitro; analiphatic or cycloaliphatic C₆-C₁₈-hydrocarbon; a chloro hydrocarbon; ora mixture or combination thereof, or sulfuric acid.
 3. A crystallineN,N′-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboxylic diimideof the form A, characterized by an X-ray powder diagram (CuK_(α)) havingsignificant lines at d values of 10.2, 9.60, 8.17, 7.60, 7.07, 6.89,6.02, 5.64, 4.89, 4.79, 4.63, 3.93, 3.81, 3.53 and 3.43 Å.
 4. AcrystallineN,N′-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboxylic diimideof the form B, characterized by an X-ray powder diagram (CuK_(α)) havingsignificant lines at d values of 15.3, 7.68, 7.32, 7.15, 5.99, 5.59,5.33, 4.98, 4.24, 3.86 and 3.235 Å.
 5. A crystallineN,N′-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboxylic diimideof the form C, characterized by an X-ray powder diagram (CuK_(α)) havingsignificant lines at d values of 10.67, 9.88, 9.36, 7.82, 7.16, 6.89,5.74, 5.49, 4.68, 4.085, 3.354 and 3.252 Å.
 6. A crystallineN,N′-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboxylic diimideof the form D, characterized by an X-ray powder diagram (CuK_(α)) havingsignificant lines at d values of 9.7, 8.6, 7.85, 6.88, 4.83, 4.13 and3.81 Å.
 7. A crystallineN,N′-bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarboxylic diimideof the form E, characterized by an X-ray powder diagram (CuK_(α)) havingsignificant lines at d values of 15.2, 14.7, 8.04, 7.76, 7.36, 6.43,5.59, 4.99, 4.25, 4.14 and 3.863 Å.
 8. A crystalline solvate ofperylene-3,4:9,10-tetracarboxylic diimide of the formula I as claimed inclaim 1, which contains 1 or 2 mol of solvent per mole ofperylene-3,4:9,10-tetracarboxylic diimide.
 9. The use ofperylene-3,4:9,10-tetracarboxylic diimides as claimed in claims 1 to 7as fluorescent dyes for coloring organic and inorganic polymericmaterials.
 10. The use of perylene-3,4:9,10-tetracarboxylic diimides asclaimed in claims 1 to 7 as emitter materials in electroopticalcomponents.